A photosensitive composition can be applied onto a substrate to form a coating film, a specific portion of the coating film is subjected to exposure by light irradiation using a photomask and then a non-exposure portion is subjected to a development treatment to remove it, thereby forming a pattern. This photosensitive composition have been used for photocurable inks, photosensitive printing plates, various photoresists, color filter photoresists for LCD, photoresists for resin black matrix, transparent photosensitive materials and the like since the photosensitive composition can be polymerized and cured by light irradiation.
The photosensitive composition usually contains an alkali-soluble resin, a polymerizable compound having an ethylenically unsaturated bond, a photopolymerization initiator and a solvent.
As the photopolymerization initiator used in the photosensitive composition, there have been known various types such as acetophenone derivatives, benzophenone derivatives, biimidazole derivatives, acylphosphine oxide derivatives, triazine derivatives and oxime derivatives.
Among these, the oxime derivatives have advantages that are almost never in color, and have high permeability, high radical-generating efficiency by UV irradiation, and excellent stability and compatibility in the composition.
Japanese Patent Application Laid-Open (JP-A) No. 61-118423, JP-A No. 1-68750 and JP-A No. 3-4226 disclose the use of α-oxooxime derivatives as a photoresist photoinitiator for photoimaging and printed wiring board, and Opt. Eng. 24 (1985) 808 and J. Opt. Eng. 27 (1988) 301 discloses the use of α-oxooxime derivatives as a photoinitiator for holography.
In particular, with regard to a photoinitiator having the structure of an oxime ester, U.S. Pat. No. 4,590,145 discloses a photoinitiation system comprising thioxanthone and an oxime ester compound, U.S. Pat. No. 4,255,513 discloses an oxime ester photoinitiation system containing p-dialkylaminobenzene used as a synergist, U.S. Pat. No. 5,776,996 discloses a photoinitiator comprising β-aminooxime with a sensitizing dye and a titanocene compound, and U.S. Pat. No. 6,051,367 discloses an oxime ether photoinitiation system having ethylenically unsaturated bonds capable of participating in the photopolymerization in the molecular structure. WO 00/52530 and German Patent Application Laid-Open No. 199 28 742 A1 describe a photosensitive composition using oxime ether, oxime ester, and particularly oxime sulfonate as a photoinitiator. WO 02/100903 A1 describes an oxime ester compound having a structure bonded with alkyl acyl ketone, diaryl ketone or ketocoumarine.
In addition to these compounds, U.S. Pat. No. 4,202,697 describes an etch resist having an oxime ester structure and U.S. Pat. No. 6,001,517 describes a positive photosensitive composition comprising an oxime ester structure as a photosensitive cure accelerator.
However, among the oxime derivative compounds used as above, the initially developed compounds have low photoinitiation efficiency and do not effective for UV-light absorption in the case of having good color properties. The oxime derivative compounds published since the latter half of the 1990s have very good improved photoinitiation efficiency, but do not sufficiently satisfy the processing time conditions that were recently tightened. In particular, the oxime derivative compounds still has difficulties in the formation of fine patterns since thick films having a high concentration pigment or a coating thickness of 2.5 μm or more have no sufficient curing degree, and patterns formed therefrom cannot exhibit CD (critical dimension) and mechanical strength required for products.
Meanwhile, a halomethyl triazine compound, which generates halogen radical when decomposed by light irradiation, has also frequently been used as the photopolymerization initiator. In particular, it is known that 2-aryl-4,6-bis(trihalomethyl)-s-triazine has relatively good sensitivity.
For example, JP-A No. 53-133428 describes the use of a triazine based compound having a bicyclic or polycyclic aromatic group or heterocyclic aromatic group, particularly preferably a naphthyl group, as an aryl group at the 2-position thereof. The triazine based compound has unsatisfactory sensitivity in the practical applications and it is required to be used in large quantities and to be irradiated by light in long-term. And it has disadvantages in that the stability of a photosensitive composition with time is lowered because of insufficient solubility into a polymerizable compound having ethylenically unsaturated bonds.
Furthermore, although it is disclosed in JP-A No. 63-70243 that the stability with time of a photosensitive composition can be improved by introducing substituents having amide bonds or ester bonds into a naphthyl group at the 2-position of a triazine based compound, the sensitivity as a photoinitiator was not satisfactory since the initiator having low molecular weight and high crystallinity is precipitated onto the coated film surface or crystallizes in the film after coating.
Known methods used to solve these problems include using initiators having strong interactions with binders, photoinitiators with large molecular weights, and multi-functional or poly-functional triazine based photoinitiators.
In conjunction with the above methods, a photoinitiator having two or more photoactive triazine groups is disclosed in U.S. Pat. No. 5,298,361. 2-Aryl-4,6-bis(trihalomethyl)-s-triazine based derivatives in which an amino group substituted phenyl group is introduced at the 2-position are disclosed in U.S. Pat. No. 4,837,128. However, these compounds have excellent photoactivities, but have limits in the applications requiring color purity since they have maximum absorbance at 350 nm or more and absorb light within the scope of visible rays. Furthermore, 2-aryl-4,6-bis(trihalomethyl)-s-triazine based derivatives in which phenyl groups coupled with simple alkyl or aryl groups by S, Se, or Te are introduced at the 2-position are disclosed in European Patent Application Laid-Open No. 271195 A1. However, these compounds have problems of compatibility with binders used in a photosensitive composition, and of sublimation in the high temperature process when alkyl groups having less carbon atoms are substituted.
Therefore, it has been desired the development of a photoinitiator having advantages of both the oxime ester compound and the triazine based compound, capable of effectively absorbing UV radiation and having excellent sensitivity and excellent high temperature process characteristics.